PAPER CLIP MOTOR EXPERIMENT TUTORIALS

How To Make A Paper Clip Motor - Experiment

Building something with our own hands often provides a new quality of insight, not to mention fun. With a few inexpensive materials, you can build your own d.c. electric motor.

The process of fiddling with your motor to get it to work well illustrates the principles of physics as no textbook description can, and watching it actually spin gives tremendous satisfaction. Putting your paper clip motor together takes only a few minutes, and it is worth it!

Materials Needed
2 paper clips
1 small, strong magnet (from Radio Shack; most refrigerator magnets are too weak)
1 C or D battery
1 yard of 20-gauge (AWG 20) coated copper wire
2 rubber bands or tape
1 small piece of sandpaper

Make a tidy wire coil by wrapping it 10 times or so around the battery. Leave a few inches of wire at both ends. Tighten the ends around the coil on opposite sides with an inch or more of wire sticking out straight from the coil to form an axle on which the coil will spin (see figure below).

Attach the magnet to the side of the battery. It may stick by itself, or you may want to secure it with a rubber band or tape. The magnet’s north or south pole should point directly away from the battery (this is the way the magnet naturally wants to go).

Bend the two paper clips and attach them with a rubber band or tape to both ends of the battery so as to form bearings on which the axle rests. The clips need to be shaped so that they make good electrical contact with the battery terminals, allow enough room for the coil to spin in front of the magnet, and keep the axle in place with a minimum of friction.

After checking the fit of the axle on the bearings, use the sandpaper to remove the red insulation coating on ONE end of the wire so that it can make electrical contact with the paper clip. At the other end, remove the coating on only HALF the wire by laying the wire coil flat down on a table and sanding only the top side.

This will interrupt the electrical contact during half the coil’s rotation, which is a crude way to reproduce the effect of commutator brushes. (Ideally, the direction of current flow through the coil should be reversed with every rotation, which would then deliver a steady torque on the coil in one direction; this is what commutator brushes do.

If direct current were allowed to flow continuously, the direction of the torque on the coil from the changing magnetic flux would reverse with every half-turn of the coil. Simply interrupting the current for half a turn interrupts the torque during just that period when it would be pulling the wrong way.

Once the spinning coil has enough momentum, it will just coast through the half-turn without power until it meets the correct torque again on the other side.)

When you place the coil on the bearings with the contact side down and current flowing, you feel it being pulled in one direction by the interaction of the fields of the permanent magnet and the coil (the “armature reaction”). Now give the coil a little shove with your finger and watch it spin.

Many thanks http://www.motors.ceresoft.org

POWER SUPPLIES FOR DC MOTORS BASIC INFORMATION AND TUTORIALS

Power supplies to dc motors may be batteries, a dc generator, or rectifiers. The permanent-magnet and miniature motors use battery power supplies. Large integral-horsepower dc motors such as rolling-mill motors use dc generators as the power supply. Most fractional-horsepower and integral-horsepower dc motors operate with rectifier power supplies. Some of the types of rectifier power supplies are as follows:

1. Single-phase, half-wave

2. Single-phase, half-wave, back rectifier

3. Single-phase, half-wave, alternating-current voltage controlled

4. Single-phase, full-wave, firing angle controlled

5. Single-phase, full-wave, firing angle controlled, back rectifier

6. Three-phase, half-wave, voltage controlled

7. Three-phase, half-wave, firing angle controlled

The NEMA standard letter designations of dc motor test power supplies are as follows:

Power supply A—dc generator

Power supply C—3-phase 6-pulse controlled rectifier (230 V L-L, 60 Hz)

Power supply D—3-phase 6-pulse controlled rectifier (with three thyristors and three diodes)

with free-wheeling diode (230/460 V L-L, 60 Hz)

Power supply E—3-phase 3-pulse controlled rectifier (460 V L-L, 60 Hz)

Power supply K—1-phase full-wave controlled rectifier with free-wheeling diode (230/115 V, 60 Hz)

When a direct-current integral-horsepower motor is operated from a rectified alternating-current supply, its performance may differ materially from that of the same motor when operated from a low ripple direct-current source of supply, such as a generator or a battery. The pulsating voltage and current waveforms may increase temperature rise and noise and adversely affect commutation and efficiency.

Because of these effects, direct-current motors must be designed or specially selected to operate on the particular type of rectified supply to be used. Armature-current form factor and ripple are two important parameters to be specified for motors which are required to operate with rectifier power supplies.

The form factor is defined as the ratio of the rms value to the average value of the armature currents. Recommended rated form factors vary from 2.0 for 1-phase half-wave rectifier supplies to 1.1 for 3 phase full-wave rectifier supplies (see NEMA MG1-14.60).

Because the letters used to identify the power supplies in common use have been chosen in alphabetical order of increasing magnitude of ripple current, a motor rated on the basis of one of these power supplies may be used on any power supply designed by a lower letter of the alphabet. For example, a motor rated on the basis of an E power supply may be used on a C or D power supply.   

PERMANENT MAGNET DC MOTORS BASIC INFORMATION

Permanent-magnet (PM) motors are available in fractional and low integral-horsepower sizes. They have several advantages over field-wound types.

Excitation power supplies and associated wiring are not needed. Reliability is improved, since there are no exciting field coils to fail, and there is no likelihood of overspeed due to loss of field.

Efficiency and cooling are improved by elimination of power loss in an exciting field. And the torque versus-current characteristic is more nearly linear. Finally a PM motor may be used where a totally enclosed motor is required for a continuous-excitation duty cycle.

Temperature effects depend on the kind of magnet material used. Integral-horsepower motors with Alnico-type magnets are affected less by temperature than those with ceramic magnets because flux is constant.

Ceramic magnets ordinarily used in fractional-horsepower motors have characteristics that vary about as much with temperature as do the shunt fields of excited machines.

Disadvantages are the absence of field control and special speed-torque characteristics. Overloads may cause partial demagnetization that changes motor speed and torque characteristics until magnetization is fully restored.

Generally, an integral-horsepower PM motor is somewhat larger and more expensive than an equivalent shunt-wound motor, but total system cost may be less.

A PM motor is a compromise between compound-wound and series-wound motors. It has better starting torque, but approximately half the no-load speed of a series motor.

In applications where compound motors are traditionally used, the PM motor could be considered where slightly higher efficiency and greater overload capacity are needed. In series-motor applications, cost consideration may influence the decision to switch.

For example, in frame sizes under 5-in diameter the series motor is more economical. But in sizes larger than 5 in, the series motor costs more in high volumes. And the PM motor in these larger sizes challenges the series motor with its high torques and low no-load speed.